Electron discharge tubes



1958 H. D. DOOLITTLE ETAL 2,366,122

ELECTRON DISCHARGE TUBES Original Filed Sept. 15, 1950 i ATTORNEYS OSEPH SKEHAN INVENTOR. HOWARD D DOOLITTLE AND BY M United States Patent 2,866,122 ELECTRON DISCHARGE TUBES Howard D. l )oolittle and Joseph W. Skehan, Stamford,

Conn., assrgnors to Machlett Laboratories, Incorporated, Sprmgdale, C0nn., a corporation of Connecticut Original application September 15, 1950, Serial No.

igg stibnozvdPateltthlrlso. 2,750,535, dated June 12,

lVl e an a lication 0 tab 3 Serial No. 538,104 pp 0 er 1955' 2 Claims. (Cl. 313-302) This invention relates to electron discharge tubes for high-frequency use, particularly to tubes of the triode or tetrode type adapted for use with external tuning circuits, such as those of the cavity type.

This application is a division of our copending application Serial No. 184,958, filed September 15, 1950, now Patent No. 2,750,535.

In recent years there has been extensive activity in the ultra-high frequency and microwave regions, extending from, say, 500 megacycles to several thousand megacycles. Special tubes of the magnetron and velocity-modulated types have been widely employed in this region, and also triodes of the conventional potential gradient modulated types such as various forms of lighthouse tubes. While tubes of the magnetron and velocity-modulated types have important applications, they are of limited flexibility. There is considerable need for improved tubes of the triode or tetrode type employing relatively closely spaced electrodes and operating on the potential gradient modulated principle. In particular, tubes of this type are required which can be effectively employed with external tuning arrangements, such as cavities, so as to permit con venient tuning over a wide frequency range, and which permit a wide frequency band to be amplified.

For many applications tubes of relatively low power output are satisfactory, and the aforementioned copending application describes such tubes which are adapted for use into the microwave region with relatively high etficiency and flexibility. The tubes are of relatively simple structure and hence of relatively low cost.

There is also need for the generation and amplification of frequencies extending into the microwave region at high power levels. relatively low power tubes may be paralleled in a single tuning arrangement. The number of tubes utilized can be selected in view of the power required, thus providing flexibility to meet widely varying requirements.

For still higher power requirements the present invention discloses tubes of the annular type which permit obtaining the necessary power with relatively simple tuning cavities, thus avoiding the complexity of tuning arrangements designed for a large number of small tubes, and facilitating the suppression of undesired modes of operation.

An important factor in the design of tubes for highfrequency use is the physical length of the electrodes in the direction of wave travel. Generally speaking, for single-ended operation, the length of the cathode in the direction of wave travel should not greatly exceed one sixteenth of a wavelength so that all portions of the cathode will be at substantially the same instantaneous potential. However, when double-ended operation is possible, the cathode length may be doubled to approximately one-eighth of a wavelength, thus increasing the emission area and power output. The present invention provides tubes capable of double-ended operation so that increased power output or higher frequency use are obtainable.

Another important factor in the design of high-frea To obtain higher power a number of stronger seals, and permit the whole tube to be heatedquency tubes is the problem of heat dissipation. sufficient anode heat dissipation is always required and the tubes of the present invention provide means for adequately cooling the anode in a simple and convenient manner.

Grid heat dissipation is also an important problem, although not so widely appreciated. In order for tubes of the potential gradient modulated type to operate at extremely high frequencies, the electrodes must be very closely spaced so as to reduce the transit time for the flow of electrons from cathode to anode. This necessitates very close spacing between the grid and the hot cathode, often two mils or less, and consequently the grid is likely to become sufiiciently hot to emit electrons, and in any event to become distorted by heat expansion. In addition, conventional Wire mesh grids provide a considerable area for the interception of electrons from the cathode, with consequent heating of the wire mesh. Inasmuch as the wires in the mesh must be very fine, heat conduction from the central portions of the mesh is often quite in adequate.

In accordance with further features of the present invention, the control electrode is made in the form of a substantially unitary plate which extends to and is connected with the walls so as to provide a path of relatively high heat conductivity from the control portion of the electrode to the exterior of the tube. Thus heat may be conducted away from the control region, rather than relying primarily on radiation for cooling. Furthermore, it is preferred to dispense with wire meshes and employ a control slot construction which eliminates the intercept areas on which electrons from the cathode may impinge.

An additional advantage of the slot construction is that in manufacturing, the spacing between grid and cathode may be established by a centering tool inserted in the slot and protruding the exact amount required. Either cathode or grid may be moved until the cathod contacts the tool, whereupon the electrode supports may be fixed in place. This is an important advantage in view of the small spacing and close tolerance required.

The reduction of lead inductance is important in highfrequency tubes. The control electrode structure just described provides a low inductance between the control area and the external terminal therefor, as well as providing a path of high thermal conductivity. The construction of the tube is such as to reduce the inductance of cathode and anode leads also.

As before mentioned, double-ended operation is highly desirable for tubes in the higher frequency regions. For such operation it is highly advantageous to equalize the impedances for both ends, so as to obtain maximum efficiency without resort to complicated compensating arrangements in the external tuning circuit, and such tubes are provided by the present invention. Furthermore, in order to permit a given tube to be operated at the highest possible frequency, it is desirable to make the distance between the active electrode surfaces and the external terminals as short as possible in order that tuning arrangements, such as the plungers of tuning cavities, may approach the electrode as closely as possible. The tubes of the present invention have a compact structure which permits the external tuning plungers to approach very close to the electrodes.

In addition to general sturdy design for mechanical strength, the structure of the tube of the present invention has been designed to facilitate initial precise alignment of the electrodes and to maintain the precise alignment in use. In particular, the tubes are designed to enable the use of envelopes having ceramic portions so as to provide a strong envelope construction including 3 to higher temperatures. Thus higher temperatures may be employed during degassing so that a purer vacuum is possible, and higher operating temperatures are possible.

Referring now to the drawing wherein like characters of reference designate like parts throughout the several views, a high power triode is shown employing unitary cathode construction for ease in assembly and permitting double-ended operation with the same impedance at each end of the tube. This ofiers considerable advantages in the design of suitable cavities for use therewith.

In the drawing:

Fig. 1 is an elevational view, partly in section, of a high power triode embodying the invention;

Fig. 2 is a horizontal sectional view taken along line 2-2 of Fig. 1;

Fig. 3 is a vertical sectional view taken substantially on line 3-3 of Fig. 2;

Fig. 4 is an enlarged perspective view of a filamentary cathode and its supporting structure; and

Fig. 5 is an enlarged perspective view of one of the slotted control electrodes.

The tube has a generally annular configuration with elongated electrodes extending in the axial direction and electron flow in the radial direction. The active electrode areas are arranged in the form of surfaces of revolution. Individual directly-heated cathodes 10, in the form of elongated ribbons, are supported between respective posts 11 and 12. Fig. 4 shows a detail of the cathode and supporting post structure. Posts 11 and 12 are mounted in individual insulating strips 13, advantageously of ceramic. The inner edge of each insulating strip is provided with a metallic covering 14 to serve as a heat shield. Also plates 15 may be placed on each side of each cathode unit as heat shields and beam-forming plates.

Mounting brackets 16 and 17 are provided at upper and lower ends of the insulating strip and connected to corresponding posts 11 and 12. Brackets 16 and 17 are soldered to brackets 18 and 19 respectively which in turn are bolted to respective conductive rings 20 and 21. Cylindrical conductive members 22 and 23 are soldered to respective rings 20-21 to form upper and lower terminals for the plurality of cathode strips. The outside of the tube envelope is completed by metal rings 24-25 soldered to cylinders 22-23 and in turn joined to metal rings 26-27. The latter rings are sealed to insulating ring 28, advantageously of ceramic.

The slotted grid structure has the general form of a surface of revolution, and is composed of individual slotted units 29 (Fig. 5). The angled ends of each slotted unit are soldered to annular rings 30-31 which in turn are joined to grid terminal cylinders 32-33. The grid and cathode structures are mounted in insulated relationship by means of ceramic rings 34-35 and metal rings 36-37.

The annular anode 38 is'provided with active electrode areas 39 arranged in the form of a surface of revolution. The'portions of the anode between the active areas 39 are cut back so as to reduce capacitance between anode and grid.

Anode 38 is joined to supporting cylinders 40-41 which serve as terminals therefor. Terminals 40-41 are sealed to annular insulating rings 42-43 which in turn are joined to the grid terminals 32-33 with the aid of metal rings 44-45.

Placing the anode on the inside of the tube facilitates cooling thereof, in that the central opening may form part of a cooling conduit. If desired, cooling 'fins extending radially inward may be employed. Of course, water coolingcan be used if desired.

' Locating the cathode structure on the outside of the tube greatly facilitates assembly-with the necessaryprecise spacing between active electrode surfaces. In-assembly, the slotted control elements '29 may be individually inserted in place with a spacer between grid and anode, and then may be soldered to supporting rings 36-31.

This insures accurate location of each grid element. Then the individual cathode, including brackets 16-17, may be inserted in place with a spacer between cathode and grid. When the proper position has been obtained, brackets 16-17 may be soldered to brackets 18-19. Bolts 46 permit removing the cathode after the soldering operation has been performed so as to remove the spacer. Thereafter, it can be bolted back in place with assurance that the spacing will be correct.

It should be noted that the tube is symmetrical with respect to a plane perpendicular to the axis and midway of the electrode structure. Thus the impedances looking into the tube from the top are the same as those looking into the tube from the bottom. This greatly facilitates double-ended operation, in that tunable cavities for upper and lower ends of the tube can have the same geometry. Excellent cooling of both anode and grid structures is provided. Furthermore, the slotted control structure, in lieu of the customary grid mesh structure, further reduces heating of the control electrode. The individual cathode and control electrode structures permit accurate spacing of all the elements in the tube.

In this invention the control electrodes have employed slots instead of wire meshes for controlling the flow of electrons. This construction is preferred for the reasons given. It is possible, of course, to employ wire meshes, etc. if desired, while retaining the other advantageous features of the invention.

It will be understood that many of the details may be altered and that other embodiments are possible within the spirit and scope of the invention.

We claim:

1. An electron discharge device for high frequency use comprising an annular anode having a pair of axially extending annular terminals, an annular control electrode encircling the anode and having a pair of axially extending annular terminals, the control electrode further having a plurality of axially extending slots therein, and a cathode structure encircling the control electrode and comprising a plurality of elongated strip cathodes each of which is located adjacent a respective slot, cathode support members extending from each end of each cathode in a direction away from the slots, a pair of cathode support rings spaced from each end of the annular array of cathodes, and a plurality of brackets removably connected to the support rings, each bracket being fixedly connected with a respective cathode support member, with the brackets connected to the support members at one end of the cathodes extending in the opposite direction from the brackets connected to the support members at the other end of the cathodes.

2. An electron discharge device for high frequency use comprising an annular cathode structure having a plurality of axially extending elongated strip cathodes, a pair of cathode supports extending from the ends of each cathode, a pair of brackets connected with and supporting respective cathode supports, a pair of annular cathode supporting members having the brackets at the ends of each cathode respectively removably secured thereto, a pair of annular cathode terminals extending in opposite directions from the supporting members and forming annular protruding portions of an envelope for the device, an annular anode structure within the cathode structure and comprising an anode having a pair of annular terminals extending in opposite directions from the anode parallel with the cathode terminals and forming annular protruding portions of the envelope, an annular control electrode structure positioned between the cathode and anode structures and comprising an annular mem erhaving a plurality of axially extending slots substantially coextensive with the respective cathodes and in substantial radial alignment therewith, and a pair of annular control electrode terminals extending in opposite directions from the annular member between and parallel References Cited in the file of this patent UNITED STATES PATENTS Harris June 11, 1940 Laidig Oct. 22, 1946 Varian Apr. 5, 1949 Woodyard et al. Apr. 5, 1949 Clark June 6, 1950 Murdock Aug. 1, 1950 Boyer et al. May 5, 1953 

